The present invention relates to a laser device, and more specifically to a device which is capable of controlling, at high speeds, the intensity of a laser beam responsive to the demands of the side where the laser is used.
The conventional device of this type can be represented by a d-c discharge-type CO.sub.2 laser which is shown in FIG. 1, in which reference numeral 1 denotes cathodes, 2 denotes an anode, 3 denotes a discharge space, 5 denotes a gas stream which is sealed at a pressure of about 200 Torr, and which is a mixture of carbon dioxide, nitrogen and helium, 6 denotes a total reflector, 7 denotes a partial reflector, 8 denotes a container, 9 denotes arrows that indicate a laser beam, 10 denotes a lens, 11 denotes a metal plate that is to be processed, 20 denotes a d-c power supply, and 21 denotes stabilizing resistors. The cathodes 1 assume the form of a needle and a plurality thereof are arrayed in the direction of optical axis. The stabilizing resistors 21 are connected to each of the cathodes 1.
The operation will be explained below.
A d-c discharge is established between the cathodes 1 and the anode 2 so as to excite the laser gas. A resonator is constituted by the partial reflector 7 and the total reflector 6, and about 10% of the energy produced by the electric discharge is emitted out of the container 8 as the laser beam 9. The metal plate 11 is irradiated with the laser beam 9 which is focussed by the lens 10. The discharge energy is supplied from the d-c power supply 20 the stabilizing resistors 21 which are provided to prevent the discharge from being converted into an arc discharge in the discharge space 3.
With the conventional device constructed as mentioned above, it was difficult to change the laser outputs at high speed because of the reasons mentioned below.
From the standpoint of the electric circuit, the stability of the d-c discharge is maintained by the stabilizing resistors 21. From the physical standpoint, the stability of the d-c discharge is maintained by an electron stream which is continuously emitted by the function of locally intense electric field of the cathode drop which is automatically formed in the vicinity of the cathodes 1. The cathode drop will be stably formed within a time period of 1 to 10 msec. In the conventional device, if an attempt was made to change the energy of discharge within a time period which was shorter than 10 msec., the discharge tended to be locally converted into an arc discharge, causing the performance of the laser device to be deteriorated. Therefore, it was extremely difficult to control at high speeds the laser output by changing the energy of discharge.
Consequently, the conventional device has generally been used as a continuously operated oscillator.
FIG. 2 schematically illustrates an example when the metal plate 11 is cut by moving it in the direction x and y at an equal speed (2 meters per minute) while being irradiated with the laser beam 9 focussed by the lens 10. In FIG. 2, a folded portion B is poorly cut compared with the straight cut portions A. This is because of the fact that the metal plate 11 is stopped for a brief period of time at the folded portion B and the laser energy is injected thereto in large amounts. To avoid this inconvenience, the laser output must be attenuated for a short period of time (for example, 5 msec.) which is required for changing the direction at a position of the folded portion B. To momentarily reduce the laser output with the conventional device, however, involves great difficulty from the standpoint of maintaining discharge stability, as mentioned above.
With the conventional laser device, as mentioned above, therefore, it was difficult to control the laser output at high speed. Accordingly, the laser device could not be satisfactorily adapted for the purpose of machining workpieces.